The invention relates to an idle position detection switch for internal combustion engines.
To control the amount of fuel supply in accordance with the opening of a throttle valve in internal combustion engines, an idle position detection switch is conventionally used. FIG. 5 shows an exemplary conventional idle position detection switch of the above type. In FIG. 5, within a substantially cylindrical housing 2 mounted on a throttle body 1 are a push rod 3, a movable contact 4 arranged at the lower end portion of the push rod 3, and a fixed contact 5 arranged so as to confront the movable contact 4. The throttle body 1 is mounted on an engine (not shown) and grounded. The push rod 3 is supported while inserted into a substantially cylindrical guide 6 so as to be inwardly slidable, the guide being disposed inside the housing 2. The upper end portion of the push rod 3 projects from an end opening of the housing 2.
A ring-like plate 7 is fitted with the inner periphery of a lower end portion of the guide 6 for the push rod 3. Inside a lower end opening of the housing 2 is an insulator 8, which is disposed at the inner periphery of the housing 2. Reference character 6a designates a resilient strip unitized with a large diameter portion 6b of the guide 6; 6c, a snap fit pawl disposed at the lower end of the resilient strip 6a; 8b, a snap fit hole, disposed on the insulator 8, for receiving the snap fit pawl 6c; 8c, a locking portion so that the snap fit pawl 6c will not fall off; 9, a fixed ring disposed at the lower end of the push rod 3; 10, a support disk which carries the fixed contact 5; 11, a terminal strip which comes in electrical contact with the fixed contact 5 supported by the support disk 10; 12a, a terminal of a lead 12 caulked by the terminal strip 11; 16, a terminal caulked by the lead 12; and 17, a connector supporting the terminal 16.
Reference numeral 13 designates a spring, and the upper portion 13a of the spring 13 extends radially inwardly to be firmly seated at a lower end of the push rod 3, so that the upper portion 13a of the spring 13 can be held while clamped between the lower end of the push rod 3 and the plate 7. Accordingly, the upper end of the spring 13 is electrically connected to the movable contact 4. The lower end portion of the spring 13 extends radially outwardly to form a large coiled portion 13b. The large coiled portion 13b is positioned at a guide groove 8d arranged at an outer peripheral portion of the insulator 8 and is so attached as to be clamped onto a stepped portion 2a of the housing 2. Accordingly, the lower end of the spring 13 is electrically connected to the housing 2. The clamping of the large coiled portion 13b onto the stepped portion 2a takes place simultaneously with firmly attaching a case 18 to the housing 2 by caulking a portion 2b. The radially and outwardly extending portion at the lower end of the spring 13 is coupled to the large coiled portion 13b by projecting out while passing through a recess formed in the insulator 8. As aforesaid, the insulator 8 has the guide groove 8d at its outer peripheral portion. In addition, the insulator 8 has a support column 8c at a position radially confronting the recess. The large diameter portion 6b of the guide 6 confronts the insulator 8 so as to come in contact therewith and encloses the spring 13, the movable contact 4, and the like therein. The large diameter portion 6b has a notched groove 6d for receiving the support column 8c of the insulator 8. Between the housing 2 and the large diameter portion 6b of the guide 6 is a wave washer 14. Reference numeral 15 designates a cover made of rubber for enclosing the case 18. On the other hand, the outer periphery of the upper end of the housing 2 is a screw portion 2c formed, so that the screw portion 2 can be screwed into a screw hole 1a arranged on the throttle body 1.
The operation of the idle position detection switch will be described next. As a valve shaft 19 of a not shown throttle valve is rotated in response to a complete closure of the throttle valve, an escalating end portion 20a of a stopper 20 causes the push rod 3 to be biased while resisting the resilient force of the spring 13, thereby bringing the movable contact 4 disposed at the lower end portion of the push rod 3 into contact with the fixed contact 5. It is at this stage that the stopper 20 is positioned. The idle position detecting current is grounded while sequentially flowing through the terminal 16, the lead 12, the terminal strip 11, the fixed contact 5, the movable contact 4, the plate 7, the spring 13, the housing 2, and the throttle body 1. As a result, the idle position can be detected.
Since the conventional idle position detection switch is constructed as described above, the current path, which includes the terminal 16, the lead 12, the terminal strip 11, the fixed contact 5, the movable contact 4, the plate 7, the spring 13, the housing 2, and the throttle body 1, is complicated. As a result, the contact resistance tends to increase, and it is likely that the load applied to the fixed contact 5 will deform or break the support disc 10.
In addition, the components involved in the above construction being large in number elevates the manufacturing cost of the switch, while the length of the lead wire contributes to impairing its applicability as a general-purpose device.
The invention has been made in view of the above circumstances. Accordingly, an object of the invention is to provide an idle position detection switch for engines, which can be constructed with less components and attempts to not only reduce the incidence of defective contacts and its manufacturing cost, but also improve its strength and applicability.